The proposed studies are aimed at the elucidation of poorly understood fetal and neonatal pathways of bile acid metabolism, and the role of monohydroxy bile acids alone or in synergy with other hepatoxic agents present in utero or at birth, such as estrogen and endotoxin, in infantile liver disorders associated with biliary excretory deficiency (cholestasis). We have recently made major advances in the extraction, separation, identification and quantitation of bile acids from biological fluids and tissues including efficient and rapid Sep-Pak C18 extraction, radial compression high performance liquid chromatography for the separation and quantitation of conjugated bile salts, field desorption mass spectrometry for the identification of intact conjugated bile acids, Sep-Pak column chromatography for separation of free bile acids and capillary gas chromatography for bile acid quantitation at the picomolar level. These highly efficient and specific analytical techniques will be used to analyze the metabolism of bile acids in fetal and newborn rats, rabbits and guinea pigs, three species which show different susceptibility to hepatotoxicity of monohydroxy bile acids and to characterize changes in bile acid metabolism and liver cell function related to estrogen and endotoxin exposure. In addition to experiments in animals, monohydroxy bile acid profiles (composition, concentration, type and degree of conjugation) will be determined in human cord blood, amniotic fluid and in blood, urine, bile and feces of women with cholestasis of pregnancy and of infants with cholestatic liver disease. The results of these studies should provide basic information about gestational and postnatal development of bile acid metabolism and increased understanding of the mechanisms involved in synthesis, detoxification, elimination and interaction of hepatotoxic biliary components. The data obtained should also provide a basis for diagnosis, therapy, and prophylaxis of infantile cholestatic disorders.